The present invention relates to the medical imaging arts. It particularly relates to computed tomography (CT) imaging employing a rotating x-ray source, and will be described with particular reference thereto. However, the invention will also find application in conjunction with other types of medical imaging including magnetic resonance imaging (MRI), positron emission tomography (PET), single photon emission computed tomography imaging (SPECT), diagnostic ultrasound imaging, and the like.
Computed tomography (CT) imaging has application in many areas involving non-invasive examination of internal features of a subject. For example, CT is applicable in security baggage examination as well as in medical imaging. In CT imaging, an x-ray source transmits a fan or cone of x-rays into an examination region. The x-rays along each ray or path through the subject are partially absorbed. Detectors arranged across the examination region from the x-ray source detect the x-rays after traversing each ray or path through the examination region. The detected x-ray intensity is characteristic of x-ray transmissiveness along the ray or, when subtracted from the pre-subject intensity is characteristic of the absorption experienced as the x-rays pass through the examination region along each ray. Each data line typically represents projection data along a fan shaped swath. Typically, the projection data is convolved and backprojected into an image representation, although other reconstruction techniques are also known.
A typical modern CT imaging scanner employs a rapidly rotating (e.g., 120 rpm) x-ray source that produces a spatially extended wedge-, fan-, cone- or otherwise-shaped x-ray beam. A two-dimensional array of x-ray detectors or a plurality of one-dimensional arrays are arranged to collect x-ray data in parallel across the area of the x-ray beam. In helical CT the x-ray source continuously rotates about the subject as the subject is simultaneously advanced through the CT examination area. The helical arrangement effectuates a helical x-ray source motion relative to the subject.
The combination of a rapid rotation rate of a spatially extended x-ray source, parallel detection across the extended x-ray beam area, and continuous helical data acquisition translates into a CT imaging scanner which generates vast quantities of projection data at tremendous data acquisition rates. Preferably, the projection data are similarly rapidly reconstructed into image representations so that the CT imaging occurs in a manner approximating real time imaging. However, past reconstruction methods and apparatuses have struggled to keep up with the data influx.
CT scanners typically include one or more racks of reconstruction hardware, each custom designed for a portion of the reconstruction process. For example, dedicated processors rebin data. One or more array processors convolve each data line with a convolution or filter function. Other dedicated hardware units backproject each filtered data line into an image memory. In spiral data reconstruction, additional hardware weights and combines longitudinally displaced but axially aligned data. Various other data manipulations are performed in other dedicated hardware components.
The reconstruction processing hardware pipeline paradigm has a number of disadvantages. It is relatively inflexible because the processing path is defined in hardware. Upgrading or expanding the reconstruction pipeline either to increase speed or to add additional capabilities requires replacement or addition of at least one hardware component. Development of new or improved pipeline features or capabilities is similarly hampered. New hardware must be configured to “fit into” the pipeline both physically (i.e., connectively) and logically (i.e., in terms of input/output data format).
Furthermore, the hardware pipeline paradigm does not readily support optimal allocation of reconstruction resources across imaging systems. Interconnection of reconstruction components of different CT imaging systems is difficult or impossible. A second CT imaging system would typically be unable to access or utilize the hardware pipeline associated with a first CT imaging scanner.
In typical CT operation, the actual scanning time is brief while considerable time is expended on performing alternative reconstructions focusing on various clinical aspects. Hence, for a CT facility having two CT scanners each having separate, independent reconstruction hardware, only about one-half of the total reconstruction processing capacity of the CT facility is typically exercised at any given time.
Yet another disadvantage of past methods and apparatus is that alternative reconstruction algorithms often need additional or different dedicated hardware in the reconstruction pipeline. When a doctor or other medical analyst wants to perform an alternative or partial reconstruction of medical CT imaging data, for example to focus in on a clinically significant image feature, the doctor or analyst implements the selected post-processing reconstruction using the same reconstruction pipeline. During this post-processing, operation of the CT imaging system is suspended. Furthermore, if the doctor's non-standard reconstruction requires alternative or additional hardware, the pipeline must be reconfigured appropriately. Conversely, if the scanner is in use for imaging, the reconstruction pipeline is unavailable to other medical personnel.
The present invention contemplates an improved apparatus and method which overcomes the aforementioned limitations and others.